Figs. 96, 97, 98.—Raising Towers on Niagara Transmission Line.
Fig. 99.—One of the Towers in Position.
The labor of erecting these steel towers was reduced to a low figure by the method employed, as shown in the accompanying [illustration]. Each tower was brought to the place where it was to stand with its parts unassembled. For erecting the towers a four-wheel wagon with a timber body about thirty feet long was used. When it was desired to raise a tower, two of the wheels, with their axle, were detached from the timber body of the wagon, and this body was then stood on end to serve as a sort of derrick. This derrick was guyed at its top on the side away from the tower, and a set of blocks and tackle was then connected to the top of the derrick and to the tower at a point about one-fourth of the distance from its top. A rope from this set of blocks ran through a single block fixed to the base of the derrick and then to a team of horses. On driving these horses away from the derrick the steel tower was gradually raised on the two legs of one of its rectangular sides until it came to a vertical position. The next operation was to bring the legs of the tower into contact with the extension pieces that were fixed in the earth and then bolt them together.
Fig. 100.—Steel Tower for Transmission Line.
The tops of the three pins that carry the insulators for each three-phase circuit are at the corners of an equilateral triangle ([Fig. 100]), each of whose sides measures six feet. The six steel insulator pins used on each tower are exactly alike, and each is swaged from extra heavy pipe. Each finished pin is 23⁄8 inches in diameter for a length of 31⁄4 inches, and then tapers uniformly to a diameter of 11⁄8 inch at the top through a length of 111⁄2 inches. This gives the pin a total length of 143⁄4 inches. In the larger part there are two 9⁄16-inch holes from side to side, and within two inches of the top there are three circular grooves each 3⁄16 inch wide and 1⁄16 inch deep. Forged steel sockets of two types are employed to attach the steel pins with the pipes. Each socket is made in halves, and these halves are secured to both the pipe and the pin by through bolts. Like all other parts of the towers, these steel pins and sockets are heavily galvanized. On each of the four corner bars of a tower the lower six feet of its length is secured to the upper part by bolts or rivets. This lower six feet of each corner bar is embedded in the earth, and the construction just named makes it easy to replace the bars in the earth when corrosion makes it necessary.
Footings for each tower are provided by digging four nearly square holes with their sides at approximately 45 degrees with the direction of the transmission line, and the shortest side of each hole at least two feet long. Centres of these holes are 14 feet 3 inches apart in a direction at right angles to the line, and 13 feet 9 inches apart parallel with the line. In hard-pan each one of the holes was filled to within 2 feet 6 inches of the top with stones, after the leg of the tower was in position, and then the remainder of the hole was filled with cement grouting mixed four to one.